Field of the Invention
The invention relates to a device, in particular a charging device, for charging an accumulator, having a charging current supply unit that can be operated in a plurality of charging modes, where a user is able to select the particular charging mode, and having a discharging device provided for at least one of the charging modes.
Description of the Prior Art
A device of this kind is already known from DE 101 07 619 A1. It is a microcontroller-controlled charging device with which the user, before the start of charging, can select from among a plurality of charging functions listed in a menu on a display. For example, in a standard charging mode, the accumulator is first completely discharged and only after this is completely charged. A charging mode can be entirely or partially composed of one or more discharging measures. On the other hand, charging modes without any discharging measures are also provided.
DE 691 23 277 T2 has disclosed a battery charging system in which a charging device that can be operated in at least two different charging modes is connected to a mobile phone that contains an accumulator to be charged and the charging modes can be selected manually via the mobile phone. The mobile phone can be provided with a device for detecting the charge state of the accumulator so that depending on the detected charge state, an associated charging mode is automatically activated. In particular, a charging mode for a slower charging is automatically activated whenever the charge state falls below a threshold value. This automatic selection and activation of a charging mode can be overridden by the manual selection via the mobile phone.
The patent application DE 10 2005 020 356 A1 describes a device, in particular a charging device, having a measuring device for detecting at least one battery parameter that depends in particular on the number of charge/discharge cycles it has undergone and therefore reflects an aging of the battery. In this way, a processing unit can establish an aging-specific charging mode that is assigned to the appropriate, current aging class of the battery. An adjusting device can be provided for manually adjusting the established charging mode, which is individually optimized with regard to the aging of the particular battery, and charging the battery accordingly.
The previous charging modes are operation-oriented. The previous charging modes and charge states—which were unspecific with regard to a subsequent (longer) storage of the accumulator—turn out, however, to be problematic, particularly in connection with lithium accumulators.
In general, it must be assumed that accumulators (rechargeable batteries) can be stored not only in the fully charged or partially charged state, but also after the complete discharging of the energy stored in the cells. Experience shows, however, that lithium-ion cells in particular and rechargeable batteries composed of them, when stored in the (almost) fully charged state, experience a more pronounced aging than is the case when stored in the partially charged or completely discharged state. This aging manifests itself in an increased internal resistance of the battery and an irreversible loss of energy storage capacity of lithium-ion batteries.
First and foremost, storage in the fully charged state accelerates the aging of lithium-ion cells so that after even one month of storage, a significant reduction in the capacity of the accumulator can occur. In order to avoid this effect, newly produced cells are stored and shipped in a partially charged state. If battery packs in use are to be stored for longer periods of time, it has up to now been advantageous to connect a consumer (appliance or external electrical load) to the lithium-ion accumulator in order to change it into a partially charged state.